1. Field of the Invention
The present invention relates to power wrenches and more specifically to power tongs for making up and breaking out threaded connections between adjoining tubular members. In particular, the invention relates to means for reducing friction at the bearing surface between the upper cage plate and the top body plate of a power tong.
2. Description of the Prior Art
Oil field tubular members, e.g. drill pipe and casing, are employed in sections which are joined together at their ends by threaded connections. Power tongs of the type herein described are utilized to make up and break out these threaded connections by securely gripping one tubular member and rotatably driving that member relative to the adjoining member. Tongs representative of present practice in the industry are described in U.S. Pat. Nos. 2,879,680; 3,180,186; 3,261,241 and 4,084,453.
When a power tong is used to grip and rotate a pipe section, a pipe-gripping mechanism, as described, for example, in U.S. Pat. No. 2,879,680, is utilized to bring a pair of jaws into contact with the pipe. The jaws are pivotally mounted by bolts which pass through the jaws. The bolts are secured at their ends to the so-called "upper and lower cage plates". The cage plates are generally arcuate plates that are adapted to rotate with the jaws when the pipe is securely gripped. The cage plates may rotate opposite plates on the tong body. Generally, the upper and lower cage plates are joined together by bolts or the like so that the entire weight of the cage plates is borne at the bearing surface between the upper cage plate and its opposing top body plate. Therefore, during rotation of the cage plates, it is desirable to reduce friction and other undesirable forces at the bearing surface between the upper cage plate and the top body plate. The friction encountered at this bearing surface can have dramatic effects on the overall efficiency of tong operation. In prior art devices the upper cage plate is typically in a metal-to-metal contact with the top body plate, thereby causing a great deal of friction during operation. The foregoing tong structure and operation is well-known to those skilled in the art and is shown, for example, in U.S. Pat. No. 2,879,680.
Consequently, there is an acute need for safe, simple and reliable means for reducing friction and other undesirable forces at the interface between a tong cage plate and its opposing tong body plate.